Non-ergodic aging and hierarchical organization in lithium-potassium tantalate crystals

The dielectric constant of K1-xLixTaO3, with x = 0.01 and x = 0.025, and specially its value at very long times, measured as a function of time (aging) at 4 K, depends on the cooling rate; this is a non-ergodic behaviour which manifests the lack of self-similarity of the phase space. The response to temperature jumps, similar to that of spin-glasses, is the signature of hierarchical organization of the phase space. For x = 0 (pure KTaO3), the behaviour is ergodic.